Teresa Sharp, a homemaker and grandmother, has lived in Hamilton County, Ohio, for nearly 30 years. A former poll worker and a Democrat, she says she has voted in every election since she was 18.

"Voting to me is, like, sacred, like my children," she said. "It lets me at least have an opinion about how I want to live in America."

Sharp is keenly aware that her vote counts. Hamilton County, which includes Cincinnati, is hotly contested in a swing state that could decide this extraordinarily close presidential race. So naturally, Sharp was surprised when she received a letter in the mail that said, "You are hereby notified that your right to vote has been challenged by a qualified elector under RC 3503.243505.19."

Her husband, Herbert, her sons, Christopher and Herbert Jr., her daughters, Aseneth and Eleanor, and her elderly aunt, all residents at the same family home in Hamilton County, also received a similar letter.

"I thought to myself that there's somebody out here trying to scare people into not voting," she said.

The letter came from the county board of elections, and was prompted by an official challenge submitted by a member of The Ohio Voter Integrity Project, a local affiliate of a grassroots organization called True the Vote. The organization believes that voter fraud is a sweeping national epidemic and has enlisted and trained an army of citizen volunteers to challenge voters in the name of what they call "voter integrity."

Their promotional and recruitment videos talk about "willful, fraudulent behavior," and, "people voting who are not who they said they were." They said they address the important need to keep elections free and fair for all citizens.

The goals sound admirable, and even patriotic, but Sharp and other Democrats say True the Vote is less about voter integrity than voter suppression, and is specifically meant to intimidate minorities, low-income people and students who might vote for President Obama.

"I was like, 'Whoa, why are they targeting my family? What did we do?'" said Sharp.

While it is legal in 46 states for any citizen to challenge another citizen's right to vote, election officials said, it very rarely happens.

But this election cycle, the challenge against Sharp was among 1,077 citizen challenges received by the Hamilton County Board of Elections alone. The challenge against Sharp incorrectly cited her property as a vacant lot, but after a hearing Hamilton County election officials threw it out.

Attempts to reach Marlene Kocher, the member of the local Integrity Project who challenged Sharp, were not successful. Other True the Vote volunteers declined to speak with us on camera.

However, True the Vote founder Catherine Engelbrecht, who travels the country speaking about voter fraud, agreed to speak with "Nightline" in her first national television interview. Engelbrecht denied the allegations that her organization was attempting to intimidate voters from the polls.

"Our goal really is to encourage citizens to get involved in the process," she said. "It has been a continued shock and disappointment, frankly, to hear these allegations that continue to be leveled at us. It's unfortunate that there are those that have tried to take this and twist it into something that it's not."